High-efficiency, ultra-low power gas sensors are provided. In one aspect, a gas detector device is provided which includes: at least one gas sensor having a plurality of fins; a conformal resistive heating element on the fins; a conformal barrier layer on the resistive heating element; and a conformal sensing layer on the barrier layer. A method of forming a gas sensor as well as a method for use thereof in gas detection are also provided.
|
11. A method of gas detection, the method comprising the steps of:
providing a gas detector device having at least one gas sensor comprising: a plurality of fins; a conformal resistive heating element on the fins; a conformal barrier layer on the resistive heating element; and a conformal sensing layer on the barrier layer, wherein the conformal resistive heating element, the conformal barrier layer and the conformal sensing layer each conforms to a shape of the fins thereby providing a plurality of gas sensor layers disposed conformally over the fins with a gap present between the gas sensor layers over adjacent fins;
heating the gas sensor via the resistive heating element; and
taking readings from the gas sensor.
1. A method of gas detection, the method comprising the steps of:
providing a gas detector device having at least one gas sensor comprising: a plurality of fins; a conformal resistive heating element on the fins; a conformal barrier layer on the resistive heating element; and a conformal sensing layer on the barrier layer, wherein the conformal resistive heating element, the conformal barrier layer and the conformal sensing layer each conforms to a shape of the fins thereby providing a plurality of gas sensor layers disposed conformally over the fins with a gap present between the gas sensor layers over adjacent fins, and wherein the gas sensor further comprises a substrate beneath the fins;
heating the gas sensor via the resistive heating element; and
taking readings from the gas sensor.
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
heating at least one of the gas sensors in the array to a different temperature from another at least one or more of the gas sensors in the array.
10. The method of
recording a time the readings are taken from the gas sensors to determine a path of a gas as the gas passes over the array.
12. The method of
13. The method of
14. The method of
15. The method of
16. The method of
17. The method of
heating at least one of the gas sensors in the array to a different temperature from another at least one or more of the gas sensors in the array.
18. The method of
recording a time the readings are taken from the gas sensors to determine a path of a gas as the gas passes over the array.
|
This application is a divisional of U.S. application Ser. No. 14/955,486 filed on Dec. 1, 2015, now U.S. Pat. No. 10,041,898, the disclosure of which is incorporated by reference herein.
The present invention relates to gas sensors, and more particularly, to high-efficiency, ultra-low power gas sensors.
There is a great need for portable low power volatile organic compound (VOC) sensors for monitoring VOC emission in today's industrial scale natural gas production. See, for example, Karion et al., “Methane emissions estimate from airborne measurements over a western United States natural gas field,” Geophysical Research Letters, vol. 40, pgs. 1-5 (August 2013) and J. Peischl et al., “Quantifying sources of methane using light alkanes in the Los Angeles basin, California,” Journal of Geophysical Research: Atmospheres, vol. 118, pgs. 4974-4990 (May 2013).
Semiconductor metal oxide based gas sensors have great potential in such applications due to their low cost and portability. However, the power consumption of such sensors is relatively high (e.g., greater than 50 mW), which hinders their application in continuous monitoring with battery power in a service time scale of years. For instance, microelectromechanical (MEMS)-based membrane gas sensors, which are currently the most advanced and of the lowest power consumption, still consume from about 6 mW to about 20 mW of power. The high power consumption of these sensors is mainly due to the requirement of operating the sensors at elevated temperatures (e.g., from about 300° C. to about 400° C.) during gas sensing in order to achieve reasonable sensitivity.
Therefore, improved low-power gas sensors would be desirable.
The present invention provides high-efficiency, ultra-low power gas sensors. In one aspect of the invention, a gas detector device is provided. The gas detector device includes: at least one gas sensor having a plurality of fins; a conformal resistive heating element on the fins; a conformal barrier layer on the resistive heating element; and a conformal sensing layer on the barrier layer.
In another aspect of the invention, a method of forming a gas sensor is provided. The method includes the steps of: patterning a plurality of fins in a substrate; depositing a conformal resistive heating element on the fins; depositing a conformal barrier layer on the resistive heating element; and depositing a conformal sensing layer on the barrier layer.
In yet another aspect of the invention, a method of gas detection is provided. The method includes the steps of: providing a gas detector device having at least one gas sensor that includes: a plurality of fins; a conformal resistive heating element on the fins; a conformal barrier layer on the resistive heating element; and a conformal sensing layer on the barrier layer; heating the gas sensor via the resistive heating element; and taking readings from the gas sensor.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.
As provided above, a significant drawback to current gas sensor technology is a relatively high power consumption, which limits their long term use in the field. Advantageously, provided herein are new innovative gas sensor designs which can achieve 100× reduction in power consumption as compared with conventional sensors.
The typical gas sensor on the market today uses ceramic or glass substrates to benefit from the low thermal conductivity of these materials. However, the heated area is relatively large: in hundreds of microns to over several millimeters in linear dimensions. There have also been efforts to try to build gas sensors on silicon substrates to utilize complementary metal-oxide semiconductor (CMOS) technology. An example of such sensors is microelectromechanical (MEMS)-based membrane gas sensors. See, for example, U.S. Patent Application Publication Number 2015/0090043 by Ruhl et al., entitled “MEMS.” There are, however, three key drawbacks of the MEMS based sensor design. First, the high thermal conductivity of the silicon (Si) substrate makes it hard to achieve power reduction due to the large amount of thermal loss through the substrate. Second, due to the chemical wet etch process limitations, a relatively large size heater is produced (several hundreds of micrometers). Third, the mechanical strength of the membrane in portable sensors is a concern.
The full potential of battery-powered gas sensors cannot be fulfilled without the successful scaling of the heater down to a few micrometers or submicron dimensions either on silicon substrate or on ceramic/glass substrates. In the present sensor design, the heater size and the sensor dimensions are substantially reduced down to micrometer scale (less than 10 micrometers in size) and even nanometer.
Advantageously, the present design can reduce power consumption substantially in three aspects. First, according to an exemplary embodiment, the commonly used Si substrate is replaced with the same thickness of silicate glass wafers. The thermal conductivity of borosilicate glass is about 1.1 watts per meter Kelvin (W/m·K). This alone can reduce heat loss of the substrate by about 100× (as compared to Si) without compromising the mechanical strength of the substrate. According to another exemplary embodiment, low thermal conductivity on silicon is achieved by creating air pockets or pores inside the silicon substrate using a dry etch process.
Second, as will be described in detail below, the heating element is woven inside the sensor fins in order to maximize heat utilization by closely patterning the fins. In this manner, the sensing area is increased by a factor of from about 5 to about 10 times for the same area of substrate. To put it in another way, heat dissipation through the substrate is reduced by a factor from about 5 to about 10 times with the same amount of tin oxide (SnO2) sensing surface as compared with a planar layout.
Third, according to an exemplary embodiment, a serpentine layout is used for the fins. A serpentine layout can scale down the dimension of total sensing area without compromising resistive path length of the sensing materials. This opens the door for miniaturization of sensors and enables array fabrication without significant cost increase.
An exemplary process for fabricating the present gas sensor is now described by way of reference to
Standard lithography and etching techniques can then be used to pattern the SOI layer, via the fin masks 104a, into individual fin portions 104b. In this example, the fin masks 104a and the patterned SOI layer portions 104b are what form the fins 104. As highlighted above, a buried insulator is present beneath the SOI layer. Thus, in this exemplary embodiment, the substrate 102 shown in
The process is, however, not limited to SOI wafer configurations. For instance, in the same manner described, the fins 104 can be patterned in a bulk semiconductor (e.g., a bulk Si wafer). To isolate the fins, an insulator (such as SiO2) can be deposited or grown on the fins, thereby forming the fin configuration shown in the figures, i.e., having an SiO2 portion 104a and an Si portion 104b.
As will be apparent from the following description, the purpose of the fins 104 is to provide a template on which a plurality of gas sensors is built. Building the sensor on a high-aspect ratio fin structure greatly increases the surface area and thereby the sensitivity of the sensors without increasing the overall sensor footprint. According to an exemplary embodiment, the fins each have a width (WFIN) of from about 20 nanometers (nm) to about 100 nm, and ranges therebetween, and a fin-to-fin spacing (SFIN) of from about 50 nm to about 150 nm, and ranges therebetween.
A resistive heating element 202 is then formed on the fins 104. See
A thin barrier layer 302 is next deposited onto the resistive heating element 202. See
A sensing layer 402 is then deposited onto the barrier layer 302. See
As provided above, one important design consideration contemplated herein is to be able to reduce power consumption of the sensors by reducing the amount of heat conducted through the substrate. Namely, if the substrate acts as a significant thermal conductor, then a greater amount of heat needs to be generated (i.e., by the resistive heating element) to achieve a given temperature, which in turn uses more power. A few different techniques are anticipated herein for reducing the thermal conductivity of the sensor substrate.
In a first exemplary embodiment, the thermal conductivity of the substrate 102 is reduced by creating air pockets 404 in the substrate 102. See, for example,
Another technique anticipated herein for reducing the thermal conductivity of the substrate is to detach the completed sensor from the bulk of substrate 102 and attach it to a low-κ substrate 502, such as a ceramic or borosilicate glass substrate. Backside polishing, spalling, vapor phase etching, or chemical etching methods can be used to detach the sensors from the bulk silicon substrate. See
According to an exemplary embodiment, a serpentine layout of the gas sensors is employed. By “serpentine,” it is meant that the gas sensor includes multiple interconnected rows of the resistive heating element 202/barrier layer 302/sensing layer 402. For instance, as will be described in detail below, in one example, the resistive heating element 202 in two adjacent rows is connected at one end of the rows. The resistive heating element 202 is connected to the next adjacent row at the opposite end, and so on, forming a serpentine layout of interconnected rows. This serpentine layout serves to balance two important design considerations, one being minimizing power consumption, and the other maximizing sensor sensitivity. With regard to minimizing power consumption—by having the heating element and sensing layer divided into distinct interconnected rows (rather than, e.g., a single heater/sensing layer over the entire footprint of the sensor), the total area of the sensing layer needing to be heated is reduced, thereby reducing the overall power consumption. However, with the serpentine layout, the sensing layer is still present across the entire footprint of the sensor, thereby maximizing sensitivity.
This serpentine layout can be achieved in a number of different ways. For instance, according to one exemplary embodiment, the sensor can be built in the manner described above. Following deposition of the sensing layer 402, the sensor can then be divided into a plurality of distinct rows. For instance, standard lithography and etching techniques can be used to divide the fins and sensor structure into multiple parallel rows. See, for example,
To form the serpentine layout, each of the patterned rows is interconnected. See
As shown in
In the same manner as described above, the barrier layer 302 (not visible) and sensing layer 402 is then deposited onto the resistive heating element 202. See
As described above, one technique anticipated herein for reducing the overall thermal conductivity of the substrate is to release the sensor from its original substrate and transfer the sensor to a low-K substrate (e.g., low-K substrate 902), such as a ceramic or borosilicate glass substrate. See
As will be described in detail below, an array of the present sensors (as shown, for example, in
Another notable benefit of an array design is that different sensors (sensitive to different gasses) can be included in the same array, thus making the data collected in the field more comprehensive. For instance, gas leaks can include more than one type of gas. As provided above, the sensitivity of the sensing layer (such as SnO2) to different gasses can vary depending on the temperature at which the sensing layer is operated (via the resistive heating element). Thus, by way of example only, different sensors in the array can be operated at different temperatures, thereby making the array sensitive to a variety of different gases.
The completed sensor 900 may now be used in the field for gas sensing. However, as highlighted above, embodiments are anticipated herein where multiple sensors are arranged as array. As described above, there are notable advantages to an array implementation. For instance, multiple sensors provide a level of redundancy, thereby increasing the overall accuracy of the measurements. Further, the detection of the path of the gas over the sensors in the array can be used to pinpoint the source (e.g., thereby enabling detection of the source of a gas leak, etc.). The array might also include different sensors (i.e., sensors for detecting different gases). In that case, the array can enable detection of different gas species (e.g., in the instance where a gas leak contains multiple gases).
Thus, according to an exemplary embodiment, as shown in
In step 1104, the sensing layer 402 in the at least one sensor is heated to a given temperature via the resistive heating element 202. As provided above, the selectivity of the sensor to different gases can vary depending on the sensor temperature. For instance, the ability of a SnO2 sensing layer 402 to detect various gases can be changed simply by varying the temperature of the sensing layer 402. For instance, at a temperature of 350° C. a SnO2 sensor can detect both methane and butane gas however, when the temperature is raised to 425° C., the same sensor is selective to detecting only butane. See, for example, Chakraborty et al., “Selective Detection of methane and butane by temperature modulation in iron doped tin oxide sensors,” Sensors and Actuators B: Chemical, vol. 115, issue 2, pgs. 610-613 (June 2006), the contents of which are incorporated by reference as if fully set forth herein.
It is notable that the individual sensors in an array can be independently heated to different temperatures, e.g., so as to regulate their sensitivity to various different gases. Thus, according to an exemplary embodiment, in step 1104 at least one of the sensors in the array is heated to a different temperature from at least one or more other sensors in the array to confer different sensing capabilities across the array.
In step 1106, readings are taken from the sensors. As described in detail above, the resistance of the sensing layer 402 changes when the sensors are exposed to a gas. For instance, in the case of a SnO2 sensing layer, the resistance of the sensing layer changes when the sensor is exposed to a certain gas(es) such as methane. The resistance of the sensing layer 402 can be measured via the sensing electrodes 802. Further, in step 1106, the readings are preferably time stamped (i.e., the time the readings are taken are recorded). As provided above, this will enable detection of the path of the gas across the sensor array. Take for instance the scenario where a gas is detected at times T1, T2, and T3 (wherein T1<T2<T3) at sensors S1, S2, and S3, respectively, in the array. It can be assumed that the path of the gas across the array is along sensors S1, S2, and S3, in that order. One can then trace back the path to approximate the source of the gas. See, for example
Any data storage, collection and/or processing may be carried out in conjunction with the present gas sensing device, for example, using an apparatus such as that shown in
Processor device 1220 can be configured to implement the methods, steps, and functions disclosed herein. The memory 1230 could be distributed or local and the processor device 1220 could be distributed or singular. The memory 1230 could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term “memory” should be construed broadly enough to encompass any information able to be read from, or written to, an address in the addressable space accessed by processor device 1220. With this definition, information on a network, accessible through network interface 1225, is still within memory 1230 because the processor device 1220 can retrieve the information from the network. It should be noted that each distributed processor that makes up processor device 1220 generally contains its own addressable memory space. It should also be noted that some or all of computer system 1210 can be incorporated into an application-specific or general-use integrated circuit.
Optional display 1240 is any type of display suitable for interacting with a human user of apparatus 1200. Generally, display 1240 is a computer monitor or other similar display.
Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made by one skilled in the art without departing from the scope of the invention.
Chang, Josephine B., Lu, Siyuan, Hamann, Hendrik F., Shao, Xiaoyan
Patent | Priority | Assignee | Title |
Patent | Priority | Assignee | Title |
4627269, | Apr 04 1984 | Cerberus AG | Method of, and apparatus for, detecting reducing gases in a gas mixture |
5635628, | May 19 1995 | Siemens Aktiengesellschaft | Method for detecting methane in a gas mixture |
5759493, | Apr 30 1996 | Arizona Instrument LLC | Apparatus for detecting a specified gas within a mixture |
5767388, | Apr 26 1995 | Siemens Aktiengesellschaft | Methane sensor and method for operating a sensor |
5866800, | Oct 26 1994 | LG SEMICON CO , LTD | Gas sensor and method for fabricating same |
8443647, | Oct 09 2008 | Southern Illinois University | Analyte multi-sensor for the detection and identification of analyte and a method of using the same |
8490467, | May 18 2007 | Life Safety Distribution AG | Thermally insulating ceramic substrates for gas sensors |
8691609, | Sep 30 2011 | Silicon Laboratories Inc | Gas sensor materials and methods for preparation thereof |
9027387, | Oct 09 2007 | UNIVERSITY OF FLORIDA RESEARCH FOUNDATION, INC | Multifunctional potentiometric gas sensor array with an integrated temperature control and temperature sensors |
20060154401, | |||
20090145220, | |||
20090249859, | |||
20110163313, | |||
20110302991, | |||
20120161790, | |||
20130036811, | |||
20130249022, | |||
20130264660, | |||
20130285682, | |||
20140208828, | |||
20150090043, | |||
20150233851, | |||
20160313288, | |||
20160334359, | |||
20170003238, | |||
20170102353, | |||
20170153198, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Nov 23 2015 | LU, SIYUAN | International Business Machines Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 046356 | /0060 | |
Nov 23 2015 | SHAO, XIAOYAN | International Business Machines Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 046356 | /0060 | |
Nov 30 2015 | CHANG, JOSEPHINE B | International Business Machines Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 046356 | /0060 | |
Nov 30 2015 | HAMANN, HENDRIK F | International Business Machines Corporation | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 046356 | /0060 | |
Jul 16 2018 | International Business Machines Corporation | (assignment on the face of the patent) | / |
Date | Maintenance Fee Events |
Jul 16 2018 | BIG: Entity status set to Undiscounted (note the period is included in the code). |
Oct 23 2023 | REM: Maintenance Fee Reminder Mailed. |
Apr 08 2024 | EXP: Patent Expired for Failure to Pay Maintenance Fees. |
Date | Maintenance Schedule |
Mar 03 2023 | 4 years fee payment window open |
Sep 03 2023 | 6 months grace period start (w surcharge) |
Mar 03 2024 | patent expiry (for year 4) |
Mar 03 2026 | 2 years to revive unintentionally abandoned end. (for year 4) |
Mar 03 2027 | 8 years fee payment window open |
Sep 03 2027 | 6 months grace period start (w surcharge) |
Mar 03 2028 | patent expiry (for year 8) |
Mar 03 2030 | 2 years to revive unintentionally abandoned end. (for year 8) |
Mar 03 2031 | 12 years fee payment window open |
Sep 03 2031 | 6 months grace period start (w surcharge) |
Mar 03 2032 | patent expiry (for year 12) |
Mar 03 2034 | 2 years to revive unintentionally abandoned end. (for year 12) |